A Unique LBBB Aberrancy

Report:

Probable supraventricular tachycardia 182/min

Right axis deviation +110o

LBBB

Comment:

The QRS complexes in V1-2 take almost 0.08” to reach the nadir of their S waves, but this is not immediately obvious on inspection. The initial QRS in V1 is isoelectric, but its true onset can be mapped up from the simultaneous V2-3 channels. And yet, the ascent of the S wave is obviously slower still; the picture in V1-3 is that of LBBB despite the delayed S wave nadir.

The diagnosis of VT can still be made at once, from the frontal plane axis of +110o and LBBB morphology. This has never been observed in aberrantly conducted spontaneous supraventricular rhythms; the only differential diagnosis is the rare combination of LBBB and RAD sometimes seen in congestive cardiomyopathy8. Indeed, LBBB-like morphology with RAD is a criterion for ventricular ectopic origin in its own right27.

Below (Fig 105a)is a later trace, in atrial flutter with variable block. There is what looks very much like rate-dependent LBBB, again with right axis deviation. The fast bits have the same rate as the putative VT. This may not mean much when antiarrhythmic drugs are given, changing the flutter rate and ventricular conduction, but all the same...

This, then, appears to be the first known (to me, at least) case of LBBB/RAD aberrancy. But, not really: there must exist patients with LBBB/RAD congestive cardiomyopathy (like this one) who get SVT or flutter.

In a different context, an SVT induced at EPS in a patient with normal heart has been reported showing transient LBBB/RAD morphology94.

105a. This trace is hardly conclusive per se, but indicates the broad-complex tachycardia in the previous trace is supraventricular, perhaps flutter with 2:1 block

106. 72 year old man with cardiomyopathy (FS 7%) and implanted cardioverter-defibrillator, curiously dormant during this recording.